US20060283007A1 - Method of manufacturing implantable wireless sensor for in vivo pressure measurement - Google Patents

Abstract

A method of manufacturing a sensor for in vivo applications includes the steps of providing two wafers of an electrically insulating material. A recess is formed in the first wafer, and a capacitor plate is formed in the recess of the first wafer. A second capacitor plate is formed in a corresponding region of the second wafer, and the two wafers are affixed to one another such that the first and second capacitor plates are arranged in parallel, spaced-apart relation.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application is a continuation-in-part of U.S. patent application Ser. No. 11/157,375, filed Jun. 21, 2005, currently pending.
TECHNICAL FIELD
• This invention relates to methods of manufacturing implanted sensors for wirelessly sensing pressure, temperature and other physical properties within the human body. More particularly, the invention concerns a method of manufacturing a wireless, un-powered, micromachined pressure sensor that can be delivered using catheter-based endovascular or surgical techniques to a location within an organ or vessel.
BACKGROUND OF THE INVENTION
• The measurement of blood pressure within the human heart and its vasculature provides critical information regarding the organ's function. Many methods and techniques have been developed to give physicians the ability to monitor heart function to properly diagnose and treat various diseases and medical conditions. For example, a sensor placed within the chambers of the heart can be used to record variations in blood pressure based on physical changes to a mechanical element within the sensor. This information is then transferred through a wire from the sensor to an extracorporeal device that is capable of translating the data from the sensor into a measurable value that can be displayed. The drawback of this type of sensor is that there must be a wired connection between the sensor and the extracorporeal device, thus limiting its use to acute settings.
• Many types of wireless sensors have been proposed that would allow implantation of the device into the body. Then, through the appropriate coupling means, pressure reading can be made over longer periods of interest. The primary limitation to these type of sensors is that the fabrication methods used to manufacture them do not provide sufficient miniaturization to allow them to be introduced and implanted into the heart using non-surgical, catheter-based techniques while maintaining the ability to communicate wirelessly with external electronics.
• An implantable sensor of this type must be assembled using the materials and fabrication methods that ensure appropriate biocompatibility and long term mechanical and electrical durability.
• One method of manufacturing a sensor capable of measuring pressure is to use a capacitor that is assembled such that one of the capacitive plates will be displaced with respect to the other as a result of exposure to externally applied stress. This displacement will result in a change in the capacitance that is proportional to the applied stress. Various patents describe the fabrication and use of capacitor-based pressure sensors. The primary limitation of many of these inventions is that the techniques used to fabricate the sensors do not lend themselves to the miniaturization necessary for it to be configured as an implantable medical device while maintaining the capability of communicating wirelessly with external electronics.
• The fabrication methodologies that have been developed in the field of Micro-Electro-Mechanical Systems (“MEMS”), however, do specifically provide the means for assembling miniaturized sensors capable of measuring a variety of properties including pressure. MEMS devices as described in prior patents traditionally use silicon as a substrate for construction of miniature electrical or mechanical structures.
• A number of patents detail pressure sensors (some capacitive in nature, some manufactured using MEMS based fabrication methods) that are specifically designed for implantation into the human body. These sensors suffer from many of the limitations already mentioned, with the additional concerns that they require either the addition of a power source to operate the device or the need for a physical connection to a device capable of translating the sensor output into a meaningful display of a physiologic parameter.
• To overcome the two problems of power and physical connection, the concept of a externally modulated LC circuit has been applied to development of implantable pressure sensors. Of a number of patents that describe a sensor design of this nature, U.S. Pat. No. 6,113,553 to Chubbuck is a representative example. The Chubbuck patent demonstrates how a combination of a pressure sensitive capacitor placed in series with an inductor coil provides the basis for a wireless, un-powered pressure sensor that is suitable for implantation into the human body. Construction of an LC circuit in which variations of resonant frequency correlate to changes in measured pressure and in which these variations can be detected remotely through the use of electromagnetic coupling are further described in U.S. Pat. Nos. 6,111,520 and 6,278,379, both to Allen et al., incorporated herein by reference.
• The device described in the Chubbuck patent is large, thus requiring surgical implantation and thereby limiting its applicability to areas that are easily accessible to surgery (e.g., the skull).
• Thus, the need exists for a miniature, biocompatible, wireless, un-powered, hermetic pressure sensor that can be delivered into the heart or the vasculature using a small diameter catheter.
SUMMARY OF THE INVENTION
• Stated generally, the present invention comprises a method for manufacturing a device for monitoring the pressure within the heart or the vasculature by implanting a pressure sensor in such locations utilizing catheter-based endovascular or surgical techniques and using extracorporeal electronics to measure the pressure easily, safely, and accurately.
• Stated somewhat more specifically, according to a first aspect of manufacturing a sensor for in vivo applications, a recess is formed in a first wafer, and a capacitor plate is formed in the recess of the first wafer. A second capacitor plate is formed in a corresponding region of a second wafer. The two wafers are mutually imposed and affixed to one another such that the two capacitor plates are arranged in parallel, spaced-apart relation.
• According to a second aspect of the invention, a method of manufacturing a sensor for in vivo applications comprises the step of providing three wafers of an electrically non-conductive material. First and second capacitor plates are formed on an upper surface of the first wafer. A third capacitor plate is formed on a lower surface of the second wafer. The first and second wafers are then mutually imposed such that the third capacitor plate is positioned in generally parallel, spaced-apart relation from the first and second capacitor plates. An inductor coil is positioned on top of an upper surface of the second wafer, and the leads of the inductor coil are electrically connected to the first and second capacitor plates. A cavity is formed in the third wafer sufficient to receive said inductor coil, and the third wafer is positioned on top of the second wafer with the inductor coil being received within the cavity of the third wafer. Finally, the second wafer is bonded to the first and third wafers.
• According to still another aspect of the invention, a method of manufacturing a sensor for in vivo applications, comprises the steps of forming a bottom plate on a wafer of electrically insulating material, forming a sacrificial layer over the bottom plate, forming a top plate on top of the sacrificial layer, and removing the sacrificial layer to leave the bottom and top plates in spaced-apart relation.
• In yet another aspect of the present invention, a method of manufacturing a sensor for in vivo applications includes the step of providing first and second wafers. A recess is formed in the first wafer, and a first plate is formed in the recess of the first wafer. A coil-receiving trench is formed in an upper surface of the second wafer, and second and third plates are formed on the upper surface of the second wafer within the perimeter of the coil-receiving trench. An inductor coil is positioned within the coil-receiving trench in the upper surface of the second wafer, and the leads of the inductor coil are electrically connected to the second and third plates on the upper surface of the second wafer. The first and second wafers are affixed to one another such that the first plate in the recess of the first wafer is in parallel, spaced apart relation to the second and third plates on the upper surface of the second wafer.
• Thus it is an object of this invention to provide a method for manufacturing an implantable wireless sensor.
• It is also an object of this invention to provide a method for manufacturing a wireless, passive micromechanical sensor that can be delivered endovascularly to a heart chamber or the vasculature.
• It is a further object of this invention to provide a method for manufacturing an implantable, wireless, passive sensor that can be delivered endovascularly to a heart chamber or the vasculature to measure pressure and/or temperature.
• Other objects, features, and advantages of the present invention will become apparent upon reading the following specification, when taken in conjunction with the drawings and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of a first embodiment of an implantable wireless sensor according to the present invention, with the sensor body shown as transparent to reveal interior detail.
• FIG. 2 is a schematic view of two pressure sensitive capacitor plates being formed in recessed trenches on two substrate wafers.
• FIG. 3 is a schematic view showing the wafers ofFIG. 2 imposed in face-to-face relation.
• FIG. 4 is a schematic view showing the imposed wafers ofFIG. 3 being laser-cut around their peripheries.
• FIG. 5 is a schematic view of an alternate embodiment of two imposed wafers in which only one of the wafers has a recessed trench.
• FIG. 6 is a schematic view illustrating a first step in a process for manufacturing wafers with capacitor plates formed thereon.
• FIG. 7 is a schematic view illustrating a second step in a process for manufacturing wafers with capacitor plates formed thereon.
• FIG. 8 is a schematic view illustrating a third step in a process for manufacturing wafers with capacitor plates formed thereon.
• FIG. 9 is a schematic view illustrating a fourth step in a process for manufacturing wafers with capacitor plates formed thereon.
• FIG. 10 shows another embodiment in which two capacitor plates are formed on one wafer.
• FIG. 11 illustrates the embodiment ofFIG. 10 showing the two capacitor plates on the single wafer connected to opposite ends of a helical inductor coil.
• FIG. 12 is a schematic view of still another embodiment of an implantable, wireless pressure sensor.
• FIG. 13 is a schematic view of a further embodiment of an implantable, wireless pressure sensor in which a three-dimensional inductor coil is built onto the top of through connection terminals on the backside of a capacitor plate substrate.
• FIG. 14 is a schematic view of another embodiment of a wireless pressure sensor in which each subsequent layer is alternately spaced slightly smaller or larger in diameter than the previous winding.
• FIG. 15 is a schematic view of a further embodiment of an implantable, wireless pressure sensor in which a three-dimensional inductor coil is built onto the surface of a cylinder.
• FIG. 16 is a schematic view of another embodiment of a wireless pressure sensor in which the pressure sensitive capacitor and three-dimensional inductor coil are formed together on one wafer.
• FIG. 17 is a schematic view showing a first step in the manufacturing process of the wireless pressure sensor ofFIG. 16.
• FIG. 18 is a schematic view showing a second step in the manufacturing process of the wireless pressure sensor ofFIG. 16.
• FIG. 19 is a schematic view showing a third step in the manufacturing process of the wireless pressure sensor ofFIG. 16.
• FIG. 20 is a schematic view showing a fourth step in the manufacturing process of the wireless pressure sensor ofFIG. 16.
• FIG. 21 is a schematic view showing a fifth step in the manufacturing process of the wireless pressure sensor ofFIG. 16.
• FIG. 22 shows a first arrangement for electrically and mechanically interconnecting a capacitor plate to an inductor coil.
• FIG. 23 shows a second arrangement for electrically and mechanically interconnecting a capacitor plate to an inductor coil.
• FIG. 24 is a schematic view of another embodiment of a wireless pressure sensor in which the pressure sensitive capacitor and three-dimensional inductor coil are formed on two wafers.
• FIG. 25 is a schematic view showing a first step in the manufacturing process of the wireless pressure sensor ofFIG. 24.
• FIG. 26 is a schematic view showing a second step in the manufacturing process of the wireless pressure sensor ofFIG. 24.
• FIG. 27 is a schematic view showing a third step in the manufacturing process of the wireless pressure sensor ofFIG. 24.
• FIG. 28 is a schematic view showing a fourth step in the manufacturing process of the wireless pressure sensor ofFIG. 24.
• FIG. 29 is a schematic view of an embodiment of a wireless pressure sensor utilizing four wafers.
• FIG. 30 is a schematic view showing a first step in the manufacturing process of the wireless pressure sensor ofFIG. 29.
• FIG. 31 is a schematic view showing a second step in the manufacturing process of the wireless pressure sensor ofFIG. 29.
• FIG. 32 is a schematic view showing a third step in the manufacturing process of the wireless pressure sensor ofFIG. 29.
• FIG. 33 is a side view of a pressure sensor and a retention mechanism of a delivery device, with the retention mechanism in a closed configuration.
• FIG. 34 is a side view of the pressure sensor and retention mechanismFIG. 33, with the retention mechanism in an open configuration.
• FIG. 35 is a side view of the pressure sensor and retention mechanismFIG. 33, with the retention mechanism in an closed configuration and shown in cross-section.
• FIG. 36 is a side view of the pressure sensor and retention mechanismFIG. 33, with the retention mechanism in an open configuration and shown in cross-section.
• FIG. 37 is a side view of a dual-coil shaft of a delivery device, with a portion of the outer coil being removed to show the inner coil.
• FIG. 38 is a side view of a delivery device comprising the retention mechanism ofFIG. 33 and the shaft ofFIG. 37, illustrating a first step in the delivery of a sensor into the wall of a septum.
• FIG. 39 is a side view of the delivery device ofFIG. 38, illustrating a second step in the delivery of a sensor into the wall of a septum.
• FIG. 40 is a side view of the delivery device ofFIG. 38, illustrating a third step in the delivery of a sensor into the wall of a septum.
• FIG. 41 is a side view of the delivery device ofFIG. 38, illustrating a fourth step in the delivery of a sensor into the wall of a septum.
• FIG. 42 is a side view of an alternate embodiment of a delivery device for delivering a sensor into the wall of a septum, with the retention mechanism of the delivery device in a closed configuration.
• FIG. 43 is a side view of the delivery device ofFIG. 42 showing the retention mechanism in an open configuration.
• FIG. 44 is an isometric view of a sensor comprising an alternate arrangement for anchoring the sensor within a lumen of a patient.
• FIG. 45 is a top view of the sensor ofFIG. 44.
• FIG. 46 is a top view showing the sensor ofFIG. 44 lodged within a lumen.
• FIG. 47 is a side cutaway view of a shaft of a delivery apparatus for implanting the sensor ofFIG. 44.
• FIG. 48 is a side view of a tether wire of a delivery apparatus for implanting the sensor ofFIG. 44.
• FIG. 49 is a side view of a core wire of a delivery apparatus for implanting the sensor ofFIG. 44.
• FIG. 50 is a side view of a guidewire of a delivery apparatus for implanting the sensor ofFIG. 44.
• FIG. 51 is a side cutaway view of a delivery apparatus comprising the components ofFIGS. 47-50 with the sensor ofFIG. 44 mounted thereto.
DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT
• Referring now to the drawings, in which like numerals indicate like elements throughout the several views,FIG. 1 illustrates asensor10 for the measurement of physical parameters. The sensor can be fabricated using micro-machining techniques and is small, accurate, precise, durable, robust, biocompatible, and insensitive to changes in body chemistry, or biology. Additionally, the sensor can incorporate radiopaque features to enable fluoroscopic visualization during placement within the body. Furthermore, this sensor is encased in a hermetic, unitary package of electrically insulating material where the package is thinned in one region so as to deform under a physiologically relevant range of pressure. The LC circuit contained in the packaging is configured so that one electode of the capacitor is formed on the thinned region. This sensor does not require the use of external connections to relay pressure information externally and does not need an internal power supply to perform its function. The pressure sensor of the current invention can be attached to the end of a catheter to be introduced into a human body and delivered to an organ or vessel using catheter-based endovascular techniques.
• Referring toFIG. 1, thesensor10 includes abody12. Thebody12 is formed from electrically insulating materials, preferably biocompatible ceramics. In a preferred embodiment, the body is comprised of fused silica. Thesensor10 comprises adeflectable region14 at the lower end of thebody12. Thebody12 further comprises alower chamber19 and anupper chamber21.
• An LC resonator is hermetically housed within thebody12 and comprises acapacitor15 and aninductor20. As used herein, the term “hermetic” will be understood to mean “completely sealed, especially against the escape or entry of air and bodily fluids.” Thecapacitor15 is located within the lowercylindrical chamber19 and comprises at least twoplates16,18 disposed in parallel, spaced apart relation. Theinductor20 comprises a coil disposed within theupper chamber21 and which is in conductive electrical contact with thecapacitor15.
• Thelower capacitor plate18 is positioned on the inner surface of thedeflectable region14 of thesensor body12. Theupper capacitor plate16 is positioned on a fixed region of thesensor body12. A change in ambient pressure at thedeflectable region14 of thesensor10 causes thedeflectable region14 to bend, thereby displacing thelower plate16 with respect to theupper plate18 and changing the capacitance of the LC circuit. Because the change in capacitance of the LC circuit changes its resonant frequency, the resonant frequency of thesensor10 is pressure-dependent.
• Beyond what has been presented in U.S. Pat. Nos. 6,111,520 and 6,278,379, covering the fundamental operating principle of the wireless pressure sensor, additional means to further sensor miniaturization is required in order to achieve an acceptable size for implantation into the heart or the vasculature. The sensor outer dimensions are constrained by the lumen size of the delivery catheter that is used to introduce the sensor. Catheter inner diameters typically range from 1-5 mm. Also, the size and shape of the sensor should minimally interfere with mechanical or hemodynamic function of the heart or vessel where it is located.
• Within these physical size constraints, one of the most significant challenges is achieving adequate coupling to the sensor inductor coil from the external readout device at the necessary distance from the outside of the body to the implant site. One method for achieving enhanced coupling is to add magnetic material to the inductor. However, this approach is not feasible in a sensor intended for in vivo use, as the magnetic material would be adverse to magnetic resonance imaging, for example. For a limited coil cross-sectional area, an increased coupling coefficient is also achievable by using a three-dimensional inductor coil configuration, as opposed to two-dimensional designs. For these reasons, a three-dimensional helicalinductor coil configuration20 is the preferred embodiment for the sensor design.
• LC Circuit Introduction
• The disclosed sensor features a completely passive inductive-capacitive (LC) resonant circuit with a pressure varying capacitor. Because the sensor is fabricated using completely passive electrical components and has no active circuitry, it does not require on-board power sources such as batteries, nor does it require leads to connect to external circuitry or power sources. These features create a sensor which is self-contained within the packaging material and lacks physical interconnections traversing the hermetic packaging, such interconnects frequently being cited for failure of hermeticity. Furthermore, other sensing capabilities, such as temperature sensing, can be added using the same manufacturing techniques. For example, temperature sensing capability can be accomplished by the addition of a resistor with known temperature characteristics to the basic LC circuit.
• The capacitor in the pressure sensor of the disclosed invention consists of at least two conductive elements separated by a gap. If a force is exerted on the sensor, a portion of the sensor deflects, changing the relative position between the at least two conductive elements. This movement will have the effect of reducing the gap between the conductive elements, which will consequently change the capacitance of the LC circuit. An LC circuit is a closed loop system whose resonance is proportional to the inverse square root of the product of the inductor and capacitor. Thus, changes in pressure alter the capacitance and, ultimately, cause a shift in the resonant frequency of the sensor. The pressure of the environment external to the sensor is then determined by referencing the value obtained for the resonant frequency to a previously generated curve relating resonant frequency to pressure.
• Because of the presence of the inductor, it is possible to couple to the sensor electromagnetically and to induce a current in the LC circuit via a magnetic loop. This characteristic allows for wireless exchange of electromagnetic energy with the sensor and the ability to operate it without the need for an on-board energy source such as a battery. Thus it is possible to determine the pressure surrounding the sensor by a simple, non-invasive procedure by remotely interrogating the sensor, recording the resonant frequency, and converting this value to a pressure measurement.
• One method of sensor interrogation is explained in U.S. patent application Ser. No. 11/105,294, incorporated herein by reference. According to this invention, the interrogating system energizes the sensor with a low duty cycle, gated burst of RF energy having a predetermined frequency or set of frequencies and a predetermined amplitude. The energizing signal is coupled to the sensor via a magnetic loop. The energizing signal induces a current in the sensor that is maximized when the frequency of the energizing signal is substantially the same as the resonant frequency of the sensor. The system receives the ring down response of the sensor via magnetic coupling and determines the resonant frequency of the sensor, which is then used to determine the measured physical parameter. The resonant frequency of the sensor is determined by adjusting the frequency of the energizing signal until the phase of the ring down signal and the phase of a reference signal are equal or at a constant offset. In this manner, the energizing signal frequency is locked to the sensor's resonant frequency and the resonant frequency of the sensor is known. The pressure of the localized environment can then be ascertained.
• Q-Factor and Packaging
• Q factor (Q) is the ratio of energy stored versus energy dissipated. The reason Q is important is that the ring down rate of the sensor is directly related to the Q. If the Q is too small, the ring down rate occurs over a substantially shorter time interval. This necessitates faster sampling intervals, making sensor detection more difficult. Also, as the Q of the sensor increases, so does the amount of energy returned to external electronics. Thus, it is important to design sensors with values of Q sufficiently high enough to avoid unnecessary increases in complexity in communicating with the sensor via external electronics.
• The Q of the sensor is dependent on multiple factors such as the shape, size, diameter, number of turns, spacing between the turns and cross-sectional area of the inductor component. In addition Q will be affected by the materials used to construct the sensors. Specifically, materials with low loss tangents will provide a sensor with higher Q factors.
• The body of the implantable sensor of the disclosed embodiment of the present invention is preferably constructed of ceramics such as, but not limited to, fused silica, quartz, pyrex and sintered zirconia, that provide the required biocompatibility, hermeticity and processing capabilities. These materials are considered dielectrics, that is, they are poor conductors of electricity but are efficient supporters of electrostatic or electroquasistatic fields. An important property of dielectric materials is their ability to support such fields while dissipating minimal energy. The lower the dielectric loss, the lower the proportion of energy lost, and the more effective the dielectric material is in maintaining high Q.
• With regard to operation within the human body, there is a second important issue related to Q, namely that blood and body fluids are conductive mediums and are thus particularly lossy. As a consequence, when a sensor is immersed in a conductive fluid, energy from the sensor will dissipate, substantially lowering the Q and reducing the sensor-to-electronics distance. It has been found that such loss can be minimized by further separation of the sensor from the conductive liquid. This can be accomplished, for example, by coating the sensor in a suitable low-loss-tangent dielectric material. The potential coating material must also meet stringent biocompatibility requirements and be sufficiently compliant to allow transmission of fluid pressure to the pressure-sensitive deflective region. One preferred material for this application is silicone rubber. It should be appreciated that use of a coating is an optional feature and is not required to practice the invention per se but such coatings will preserve the Q of the sensor which can prove advantageous depending on the intracorporeal location of the sensor,
• There are various manufacturing techniques that can be employed to realize sensors according to the current invention. Capacitors and inductors made by a variety of methods can be manufactured separately, joined through interconnect methods and encapsulated in hermetic packaging. In one embodiment, the pressuresensitive capacitor15 and the three-dimensional inductor coil20 are formed separately and joined together to form the LC circuit. In another embodiment, the capacitor and inductor coil can be manufactured integral with one another. Additionally, there are several methods to create these discrete elements and to join each discrete element to create the final sensor. The following examples are provided to illustrate important design considerations and alternative methods for creating these discrete sensor elements but should not be construed as limiting the invention in any way.
• Coil Description:
• Referring toFIG. 12, theinductor coil320 is comprised of theinductor coil body322 and the coil leads324. Numerous parameters of the inductor coil can be varied to optimize the balance of size and electrical properties of the circuit, including the materials, coil diameter, wire gage, insulation thickness, number of coil windings, and cross-sectional area of the coil body. The material comprising the coil must be highly conductive and also biocompatible. Suitable materials include, but are not limited to, gold, copper, and alloys thereof.
• It is preferable in the practice of the disclosed invention to minimize or eliminate changes in resonant frequency of sensors of the invention due to factors other than capacitance in order to reliably correlate the shift in resonant frequency with a change in distance between the capacitor plates XX. Thus, it is important that theinductor coil320 in sensors of the current invention maintain a high degree of mechanical stability as a change in coil position relative to the capacitor or a change in coil configuration will cause the resonant frequency of the device to change. There are many ways to immobilize theinductor coil320 of the present invention. If the wire used to construct the coil is sufficiently strong, the coil can be self-supporting, also known as an “air core” configuration. A solenoid coil is another suitable configuration. If the wire is not sufficiently strong to maintain its intended configuration during assembly and in use, the coil can be formed around a central bobbin comprised of a suitable material. Such bobbins can be configured to be mechanically fixed to any surface or combination of surfaces defining the coil receiving trench via a press fit. Alternatively, the coil can be wound on a thermoplastic bobbin where the thermoplastic material can be subjected to sufficient heat to cause flow to encapsulate and/or adhere to the surface of the coil receiving trench.
• Alternatively, a thermosetting or thermoplastic polymer with good high temperature characteristics, low loss tangent, and, optionally, low dielectric constant material can be used to support the coil. The polymer should also be highly inert, have excellent aging resistance and exhibit substantially no moisture absorbance or outgassing. With the use of a thermosetting material, the polymer is applied to the coil in liquid form and allowed to cure or otherwise harden. Thermoplastic materials can be preformed and inserted between the coil and at least one coil receiving trench wall and subsequently heated to achieve sufficient flow to encapsulate and/or adhere to the coil and at least one coil receiving trench wall.
• Polyimide, fluorinated polymers, glass frit, ceramic paste and liquid crystal polymer are examples of suitable materials for immobilizing theinductor coil320 due to their thermal, electrical, and mechanical properties. However, manufacturing processes achieving substantially similar results that involve lower processing temperatures would make other material choices desirable, such choices being obvious to one skilled in the art.
• The wire from which the coil is formed can be solid wire, bundled wire or cable, or individually insulated stranded wire.
• The wire gage, coil diameter, cross-sectional area of the coil body, and number of windings all influence the value of inductance and the detection range of the circuit. As any of these properties increase, so do the size and the inductance of the coil, as well as the sensor-to-electronics distance. To specify an inductor coil for use in the sensor, size considerations must be balanced with those of inductance and Q.
• A small scale three-dimensional inductor coil can be formed in a variety of ways. It can be created conventionally. One such method is machine coil winding of small diameter insulated magnet wire, as shown inFIG. 1.
• In another embodiment, shown inFIG. 13, a three-dimensional inductor coil420 is built onto the top of one of the throughconnections terminals480 on the backside of thecapacitor plate substrate442, using integrated circuit processing techniques and a multitude of layers. Thiscoil420 can be defined and supported by photo-definable dielectric material such as photo-definable polyimide. In the disclosed embodiment, the coil is free standing in air, supported by same-material mechanical elements that are strategically positioned to minimize the effect of the supporting mechanical elements on the electrical function of the coil.
• In this approach it is desirable to minimize the number of design layers to improve batch process yield and to reduce processing time. In a conventional configuration, such as that shown inFIG. 13, a spacing layer is required between each winding, making the number of layers required equal to two times the number of windings. In oneversion500 of the three-dimensional coil design, an example of which is shown inFIG. 14, eachsubsequent coil510 is alternately spaced slightly smaller or larger in diameter than the previous winding. This configuration creates a small separation betweenadjacent coils510 in the x-y plane, eliminating the need for an extra vertical spacing layer in between windings. This configuration results in a number of coil windings equal to the number of layers, which is more practical for manufacturing using a MEMS approach.
• In yet anotherembodiment550, shown inFIG. 15, a three-dimensional inductor coil555 is built onto the surface of acylinder560 of an appropriate material such as, but not limited to fused silica. A conductive layer is first applied to the surface of thecylinder560. Then a mold is formed onto the surface so that parts of the underlying conductive surface are exposed and some are covered. A metal may then be formed onto the exposed areas by electroplating, sputtering or vapor deposition. The exposed area forms a helical trench that extends along the surface of the cylinder, thus realizing an inductor coil.
• Capacitor Description
• Referring now toFIG. 2, the pressuresensitive capacitor plates16,18 are formed on twoseparate substrate wafers40,42 in recessedtrenches44. At least one of thewafers40 has a substrate thickness in theregion46 of thecapacitive plate16 such that sufficient plate deflection occurs due to external pressure change, resulting in a sufficient change in resonant frequency per unit pressure (mm Hg) once the LC circuit has been created. If necessary, the thickness of thewafer40 in theregion46 can be reduced by suitable chemical or mechanical means, as indicated by the dashedline47, to provide the desired range of deflection.
• As shown inFIG. 3, thewafers40,42 are bonded together such that the capacitive plates are16,18 parallel and separated by a gap on the order of 0.1-10 microns, preferably 0.1-2 microns.
• The performances of the sensor, especially the propensity of its capacitance and, in turn, its resonant frequency to change as a response to an environmental pressure change, are closely related to few fundamental geometrical considerations. Widening or elongating the deflective region will augment its mechanical flexibility, and, in turn, the pressure sensitivity of the sensor. Decreasing the thickness of the deflective area will result in similar improvements. However, thinner deflective region can become too fragile or otherwise more sensitive to systemic response from the host-organism other than changes in mean and pulsatile blood pressure (ex: hyperplasia, tissue overgrowth, etc.). Reducing the gap, while maintaining adequate deflective region thickness, offers a complementary alternative to insufficiently low sensitivity. As the initial value of the gap is shrinking, the motion of the deflective region relative to the initial gap becomes proportionally more important. This results in a greater change in capacitance for a given stimulus, therefore enhancing the pressure sensitivity. While relevant sensitivity can be achieved with initial air-gap ranging from 0.1 to 10 micrometers, initial air-gaps ranging from a 0.1 to 2 micrometers are preferable.
• To insure adequate pressure range, the value of the maximum deflection under maximum load (indexed, for exampled, on physiologically relevant maximum pulsatile blood pressure values, at relevant location in the host-organism) ought to be, in theory, inferior or equal to the value of the initial gap. In practice, limiting the maximum deflection under maximum load to represent only a fraction of the initial gap (ex: 0.6 micrometer for a 1 micrometer initial gap) will ease the fabrication constraints and result in a more robust and versatile sensor.
• One suitable method for creating the pressure sensitive capacitor is by electroplating theindividual plates16,18 in the recessedtrenches44 on asubstrate wafer40,42 to a given height H1, H2 that is less than or equal to the depth D1, D2 of therespective trench44. When the wafers are bonded together the capacitive plates are generally separated by the difference between the sum of the trench depths and the sum of the plate heights, (D1+D2)−(H1+H2). An inherent variation in the height of the plates and the required range of deflection for the full operating pressure range are parameters, which determine the initial separation distance (a.k.a. the gap).
• FIG. 4 illustrates the assembled wafers and capacitor plates laser-cut around theirperipheries48, reducing the capacitor to its final size and hermetically fusing the two wafers together at50. A CO2 laser can be used at a peak wavelength of about 10 microns if the substrate is fused silica. Power must be sufficiently large to cut and fuse the wafers together, while at the same time being sufficiently small that the internal components of the sensor are not damaged by excessive heat.
• In an alternate method, the wafers are pre-bonded using glass frit to produce a hermetic seal around the cavities. In this method, the laser cut only releases the sensors from the wafer, and does not provide the primary means of creating the hermetic seal. Other suitable methods of hermetically sealing the wafers include, but are not limited to, adhesives, gold compression bonding, direct laser bonding, and anodic bonding.
• In an alternate embodiment illustrated inFIG. 5, oneplate18 is formed on asubstrate wafer142 having atrench144 with a depth greater that of thetrench44 in thesubstrate wafer40. Theother plate16 is formed on the inner surface of awafer140 without a trench. When imposed in face-to-face relation, theplate16 is received into the lower end of thetrench144 with theplates16,18 disposed in parallel, spaced-apart relation.
• To achieve smaller gap separation distances on the order of 0.1-2 microns, revised processing methods are employed to bring additional control to the variation in height across theconductive plates16,18. One method is as follows: theconductive plate16,18 is built to a target height that slightly exceeds the depth of therecess trench44, as shown inFIG. 6. In the disclosed embodiment the plates are formed by electroplating. Preferred materials for the plates are copper, gold, and alloys thereof. After building the plates, eachconductive plate16,18 is polished using chemical/mechanical polishing (CMP) to planarize and reduce the height of the plate until it is less than the depth of the trench by the desired amount, as shown inFIG. 9.
• Another method also begins with theplates16,18 formed to a height that slightly exceeds the depth of thetrenches44, as shown inFIG. 6. Themetal capacitor plates16,18 are mechanically polished to planarize the metal surface down to the surface of thesubstrate40,42, as shown inFIG. 7. Following this step, the metal plates are chemically etched by a selective etchant to the height indicated by the dashedline56 inFIG. 8 to achieve the desired difference in height between the height of theplate16,18 and the depth of thetrench44, as shown inFIG. 9.
• Still another method for forming the plates is physical vapor deposition (PVD), also known as thin film deposition, in conjunction with photolithography. PVD is used to deposit a uniform layer of metal, sub-micrometer to tens of micrometers thick, on a wafer. Subsequently a layer of photoresist is deposited, a mask is used to pattern the photoresist, and a selective etching technique is utilized to etch away the extra metal and to define the desired pattern. Other methods of defining the metal pattern can be utilized, such as, shadowmasking, a method well known in the art.
• In one approach, shown inFIGS. 10 and 11, a pressuresensitive capacitor215 can be formed by separating the bottom conductive pad into twoseparate regions218A,218B that capacitively couple to one another via a common thirdconductive region216 on the pressure sensitive deflective region. Theinductor coil20 is then electrically connected as shown inFIG. 11, onelead22 of thecoil20 to thefirst region218A, and theother lead24 of thecoil20 to thesecond region218B.
• When the split-plate design is employed for one side of the capacitor, as shown inFIG. 11, thesplit plates218A,218B are preferably located on the fixed side of the capacitor (i.e., opposite the pressure-sensitive side), because the electrical/mechanical interconnects made to the split plates in order to complete the LC circuit are less prone to mechanical failure when the surface to which they are mechanically attached does not deflect or move repetitively.
• In yet another embodiment, shown inFIG. 12, the plate on thetop wafer42 is separated by a dielectric into twoconductive regions318A,318B, with oneregion318B substantially larger than the other318A. After bonding together of the twowafers40,42, the smallerconductive region318A is electrically connected to the outer edge of the pressuresensitive plate316, spanning the air gap with a laser weld that is performed through the substrate material. The laser wavelength is selected so that it is passes through the substrate material with minimal energy absorption, but heats the conductive plate sufficiently to produce the weld connection between the top andbottom plates316,318A.
• Interconnects and Methods
• It will be appreciated that sensors embodied by the current invention can have capacitive and inductive elements maintained in separate hermetic cavities or that these elements may be contained in a single hermetic cavity.
• In one embodiment, the pressuresensitive capacitor15 needs to be connected to the three-dimensional inductor coil20 while maintaining a hermetic seal around the internal cavity that defines the separation gap between thecapacitive plates16,18. This can be achieved by using a variety of through-wafer interconnection methods, familiar to those skilled in the art. Referring toFIG. 22, through holes orvias660 are formed in anupper wafer662 to provide mechanical and electrical access to a pair ofupper capacitor plates664,666. The wafer through-holes can be formed before or after plate formation using some combination of the following techniques: laser drilling, chemical (wet) etching, conventional or ultrasonic machining, or dry etching. As shown inFIG. 22, thevias660 can optionally be filled with gold, copper, or other suitable conductive material to form through-wafer interconnects668 in conductive communication with thecapacitor plates664,666. The through-wafer interconnects668 thus form a hermetic seal. Leads from an inductor coil (not shown) are attached to the through-wafer interconnects668 to place the leads in conductive communication with thecapacitor plates664,666.
• Referring toFIG. 23, through holes orvias680 are formed in anupper wafer682 to provide mechanical and electrical access to a pair oflower capacitor plates684,686. Electrical connections to thelower capacitor plates684,686 will be accomplished through leads of the inductor coil (not shown) or through wires or other suitable conductive means.
• Thermosonic or ultrasonic bonding can be used to connect the inductor coil to either an electrode of a capacitor or a through-wafer interconnect. Thermosonic and ultrasonic bonding are types of wire bonding used for metal wires including, but not limited to, gold wires. Typical temperatures required for thermosonic bonding are between 125-220° C., and bonding occurs when a combination of static and ultrasonic mechanical and thermal energy is delivered to the metallic coil wire to be bonded to a metal surface. Ultrasonic bonding is performed just as thermosonic bonding but without the use of heat. Useful materials for the metallized bond sites and coil comprise gold, copper and aluminum and alloys thereof. Bonds can be formed between certain dissimilar metals as well as between all like metals, and such combinations are widely known in the art.
• If the metal or metal alloy used for the coil has a dielectric (e.g., polymer) coating, the coating must be removed prior to bonding. The coating can be removed to expose the metal at the adhesion point so that bonding can occur by either mechanical or chemical means. Alternatively, the parameters (e.g. time, heat, pressure) of the thermosonic bonding process can be altered and the geometry of the bonding tool modified so that reliable mechanical and electrical interconnects are created. Such modifications cause the coating material to be pushed aside, exposing the metal at the bonding site and extruding the wire slightly. This latter technique provides certain advantages because it reduces the number of manufacturing steps.
• An alternate method of conductively connecting the coil to the capacitive plates is the solder bump. Solder is applied to the metal-metal interface of the coil and electrode or interconnect to form a mechanical and electrical connection. This method can be used for capacitor plate or through-wafer interconnections. Lead-free solder should be used for biocompatibility. Connection can also be achieved through IC processing techniques, which allow for plates and coils to be formed in electrical contact with one another. Finally laser welds, as previously discussed, can be used to achieve electrical/mechanical interconnects.
EXAMPLE 1
• FIG. 16 illustrates a surface micromachined, capacitor coupledsensor600. Thecapacitor structure602 comprises at least twoplates604,606, at least one604 of which is built directly atop afirst wafer608. Thisplate604 will be referred to as the bottom plate. The region of thewafer608 where thebottom plate604 is built will be referred to as thedeflective region610. If necessary, the thickness of thewafer608 in the region of thedeflective region610 can be reduced in thickness to enhance its deformability.
• Theother plate606 is suspended above thebottom plate604. Thetop plate606 is mechanically anchored to the deflective region by pillar-like supportingelements612 located at the periphery of thebottom plate604. Bottom andtop plates604,606 are electrically insulated and physically separated from one another by anair gap614. Thetop electrode606 mechanical design, material and dimensions are carefully chosen so that the suspended part of the electrode does not structurally deform under its own weight or creep over time.
• Acoil616 of relevant geometry and inductance value is built or assembled using, as an example, any of the methods described herein. Its terminals are electrically and mechanically connected to either one of theopposite plates604,606 of thecapacitor602. Acapsule618 or other form of hermetic surrounding is used to encapsulate both thecoil616 andcapacitor602.
• To achieve the desired pair of fixed and suspendedplates604,606, the fabrication process of the disclosed embodiment employs a technique known in the art as “sacrificial layer.” A sacrificial layer is a structural layer that remains buried throughout the fabrication process under various layers of material until it can be removed, releasing the structures and layers built on top of the sacrificial layer. Once removed, a void remains in place of the sacrificial layer. This void forms the air gap that separates top from bottom plate(s).
• A sacrificial layer must abide by at least two rules: (1) it must remain unaffected (no cracking, peeling, wrinkling, etc.) during the entire fabrication process until it is removed, and (2) selective and efficient removal techniques must exist to remove it without adverse consequences to any remaining structures.
• Referring now toFIG. 17, the fabrication of thecapacitor602 starts with the creation of thebottom plate604 on thewafer608, using physical vapor deposition and photolithography. The backside of thewafer608 is optionally thinned to enhance compliance in thedeflective region610 of the wafer at the location of thebottom plate604 so as to facilitate deflection when a force or a pressure is applied.
• The anchoringsites612 are defined at the periphery of thebottom plate604. Anchoringsites612 are small is enough to represent only a fraction of the footprint of either bottom ortop plate604,606. However, they are big enough to insure reliable mechanical anchoring for thetop plate606.
• Referring now toFIG. 18, alayer630 of material with desirable physical and chemical traits is deposited onto thewafer608 over thebottom plate604 and the anchoringsites612 to serve as a sacrificial layer. The sacrificial material is, but is not limited to, a thin film of photo-definable polymer (the first polymer layer). The thickness of the polymer is tuned by altering the conditions during deposition. Film thicknesses ranging from fractions of micrometers to tens of micrometers are achieved routinely. To insure that thelayer630 of photo-definable polymer remains unaffected (no cracking, peeling, wrinkling, etc.) during the entire fabrication process until it is removed, proper curing and cross-linking precautionary steps must be taken.
• With further reference toFIG. 18, using photolithography,windows632 are opened in thefirst polymer layer630. The window geometry and in-plane location corresponds to those of the anchoringsites612. Because the photo-definable polymer has a non-null thickness, each opening (a.k.a. window) in the first polymer layer is surrounded bysidewalls634 which height corresponds to the thickness of the first polymer layer.
• A thin filmmetallic layer640 is then deposited on top of thesacrificial layer630, as depicted inFIG. 19. This layer comprises a seed layer, as it will provide a site upon which electroplated metals can grow later on. The method of deposition should insure that themetallic film640 evenly coats the upper surface of the sacrificial layer630 (the first polymer layer) as well as thesidewall634 and the bottom areas of thewindows632 previously defined in the sacrificial layer.
• Referring now toFIG. 20, asecond layer650 of photo definable polymer (the second polymer layer) is deposited and patterned using photolithography. During this process, selected regions are removed from the surface of the substrate, defining new windows652 (large openings) in thesecond polymer layer650 without affecting any other previously deposited layer (especially the first polymer layer630). The in-plane geometry of the new windows represents the in-plane geometry of the top electrode606 (FIG. 17). The geometry of the new windows extends to encompass the geometry and location of theanchor sites612.
• Regions where the photo definable polymer has been removed are subjected to a method known as electroplating. In that fashion, metals like copper or gold can grow and adhere in the presence of the seed layer. The electroplating occurs at the same time at the anchoring sites, on the sidewalls, and on any other region exposed through windows opened in the second polymer layer. The resulting structure is a continuous electroplatedfilm660 of the desired thickness. The thickness can range from few micrometers to few tens of micrometers. Electroplated copper is preferred for its ease of deposition and low cost.
• Next, as shown inFIG. 21, thesecond polymer layer650, themetal layer640, and thesacrificial layer630 are removed using wet or dry selective removal techniques. The preferred removal technique for both thesecond polymer layer650 and thesacrificial layer630 is wet dissolution in appropriate solvents such as acetone. At this point, both bottom andtop plates604,606 are formed. Thetop plate606 is suspended above thebottom plate604 and separated from it by anair gap614, which corresponds to the thickness of the first polymer layer.
• As the fabrication of the sensor continues, thecoil616 is built or assembled using any of the methods described herein. Its terminals are electrically and mechanically connected to either one of theopposite plates604,606 of thecapacitor602. Finally, as shown inFIG. 16, thecapsule618 or other form of hermetic surrounding is assembled onto thewafer608 to encapsulate thecoil616 andcapacitor602.
EXAMPLE 2
• A variation on the two-wafer design is shown inFIGS. 24-28. Asensor700 comprises a thickupper wafer702 and a thinnerlower wafer704. The thinlower wafer704 comprises the pressure-sensitivedeflective region portion706 of thesensor700. Anotch708 is optionally formed in theupper wafer702 to accommodate an anchor, such as a corkscrew, hook, barb, or other suitable stabilization means. The notch can be created on the backside of the wafer directly if the cap is sufficiently thick to accommodate the notch and a separation distance between the bottom of the notch and the coil body without causing any parasitic, deleterious electromagnetic or mechanical effects on the sensor function. Alternatively, the notch can be created by using wet or dry methods in a separate wafer or plurality of wafers and then bonded to the backside of the sensor. The notch can have a variety of regular or irregular geometries and can have rough or smooth sidewalls-any configuration achievable by conventional technologies that would impart some advantage or feature to assist in fixing the anchor mechanism to the sensor.
• Acapacitor710 comprises alower plate711 formed on the inner surface of thelower wafer704 and an opposing pair ofupper plates712,714 formed on the lower surface of theupper wafer702. Achannel716 is formed in theupper wafer702 to receive aninductor coil718. Theinductor coil718 includesleads720 that conductively connect the opposite ends of the coil to theupper plates712,714.
• Manufacture of thesensor700 will be explained with reference toFIGS. 25-28. Referring first toFIG. 25, a dicingtrench730 is formed in the lower portion of the upper wafer702 (shown inverted for the manufacturing process). The dicingtrench730 is a feature, which comprises a reduction in thickness of thewafer702 along a line that defines the perimeter of thesensor700. The dicingtrench730 is advantageous where reduction of the amount of energy transferred to the sensor during dicing is needed, for example, to protect the sensor from heat damage when dicing with a laser. When the wafer thickness is reduced, less energy is required to cut the sensor from the rest of the wafer, and thus less thermal energy is transferred to the critical components of the sensor.
• As can also be seen inFIG. 25, thechannel716 is formed in the upper surface of theupper wafer702. Thelower capacitor plates712,714 are formed on the upper surface of theupper wafer702.
• Referring now toFIG. 26, arecess732 is formed in the upper surface of thelower wafer704. The recess optionally includestroughs734 for providing clearance for theleads720 of the inductor coil718 (FIG. 24). Thelower capacitor plate711 is formed in the base of therecess732 in the upper surface of thelower wafer704.
• Referring now toFIG. 27, theinductor coil718 is introduced into theannular recess716 of theupper wafer702. The two leads720 of theinductor coil718 are connected to theupper capacitor plates712,714.
• Referring toFIG. 28, thelower wafer704 is now inverted and positioned atop theupper wafer702. A laser is then used to cut and simultaneously heat bond thewafers702,704 at thelines750 to complete fabrication of thesensor700. Because of the presence of the dicingtrenches730, the laser need cut through only a thickness corresponding to thedouble arrow752. This shallow cut minimizes the amount of thermal energy transferred to the internal components of the sensor.
EXAMPLE 3
• FIGS. 29-32 depict an embodiment of asensor800 manufactured from four stacked wafers,802,804,806, and808. Thebottom wafer802 comprises the pressure-sensitivedeflective region810 and a pair ofcapacitor plates812,814 formed on its upper surface. Thesecond wafer804 comprises acapacitor plate816 formed on its lower surface and a pair of through-holes818 for electrical connections. Thethird wafer806 comprises acylindrical cavity820 for accommodating aninductance coil822.Leads824 of theinductance coil822 extend through theholes818 in thesecond wafer804 and connect to thecapacitor plates812,814. Thefourth wafer808 fits atop the third wafer to provide a sealed structure.
• FIG. 30 illustrates a first step in the process for manufacturing thesensor800. Arecess830 is formed in the upper surface of the bottom wafer. Then, as shown inFIG. 32, theplates812,814 are formed in the base of therecess830. Referring toFIG. 32, theplate816 is formed on the upper surface of thesecond wafer804, and the throughholes818 are formed at the periphery of theplate816. The second wafer is then inverted and stacked on top of the first wafer.
• Thereafter, thecoil822 is positioned atop the second wafer, and electrical connections are made through theholes818 to thelower plates812,814. After formation of the pressure sensitive capacitor and inductor coil and connecting them together, hermetic encapsulation of the pressure sensitive cavity and inductor coil is performed. Thethird substrate wafer806 is prepared with thedeep recess820, sufficient to contain theinductor coil822. Therecess820 can be formed in a variety of ways, including laser rastering, glass machining, and ultrasonic machining. Thisthird wafer806 is bonded to thesecond wafer804 and subsequently, the sensors are cut out using a laser to release the sensors from the wafer stack and form the hermetic seal in the process of the cut.
• Delivery of the Sensor
• The sensors described above can be adapted for use within an organ or a lumen, depending upon what type of attachment or stabilizing means is employed.FIGS. 33-36 illustrate asensor1001 suitable for use within an organ such as the heart. Thesensor1001 has a generallycylindrical body1002 that hermetically houses the capacitor and inductor elements previously described. Thesensor1001 further has a pressure sensitive surface1003 (FIGS. 35 and 36) on one end of thecylindrical body1002 and a screw-type anchoring device1004 extending upward from the opposite end of the body.
• FIGS. 33-41 illustrate a first embodiment of a delivery device1000 (FIGS. 38, 40, and41) for implanting apressure sensor1001 in a heart chamber. Thesensor1001 has a generallycylindrical body1002 that houses the capacitor and inductor elements previously described. Thesensor1001 further has a pressure sensitive surface1003 (FIGS. 35, 36, and41) on one end of thecylindrical body1002 and a screw-type anchoring device1004 extending upward from the opposite end of the body. Aretention mechanism1005 of thedelivery device1000 comprises a “clamshell”housing1006 wherein left andright housing halves1008,1010 are resiliently deformable with respect to one another, much in the manner of a clothespin. Thehousing1006 has a recess1012 (FIGS. 35 and 36) formed in its upper end, dimensioned to receive thesensor1001 therewithin. A reverse-threadedbore1014 is formed in the lower end of thehousing1006, and asmooth counterbore1016 is formed in the lower end of thehousing1006 coaxially with the threadedbore1014.
• With further reference to thedelivery device1000, ascrew1018 has a reverse-threadedshaft1019 and ascrew head1020. Thescrew head1020 is mounted to the upper end of a dual-coil, flexible,torqueable shaft1022. As can be seen at1024 ofFIG. 37, a portion of theouter coil1026 is removed for purposes of illustration to show theinner coil1028, which is counterwound with respect to theouter coil1026.
• The reverse-threadedscrew1018 threadably engages the reverse-threadedbore1014 in the lower end of theretention mechanism1005. As thescrew head1020 advances into thesmooth counterbore1016 in the base of thehousing1006, the lower ends of the twohousing halves1008,1010 are spread apart. This causes the upper ends of thehousing halves1008,1010 to close together, thereby grasping thesensor1001.
• Referring now toFIGS. 38-41, delivery of thesensor1001 of the invention to a heart chamber may be accomplished as follows. The physician gains access into a vein that is suitable for access into the right ventricle using methods such as the Seldinger technique. Examples of these access sites would be the right jugular, left subclavian, or right femoral veins. A guidewire is advanced into the right ventricle. A large vessel introducer with an adjustable hemostatic valve is inserted over the guidewire and advanced until its tip is positioned in the right ventricle.
• Thesensor1001 is mounted to thedelivery device1000 with the longitudinal axis of the device oriented normal to the pressure-sensitive surface of the sensor and with the anchor orstabilizer1004 facing the distal end of theshaft1022. Thesensor anchor1004 can be covered with a soluble, biocompatible material, or a thin, retractable diaphragm cover (not shown). The purpose of such covering is to conceal the anchoring mechanism orstabilizer1004 and to protect the heart from inadvertent damage during sensor positioning prior to engaging the anchoring mechanism (which, in the case of the disclosedsensor1001 is configured to engage the tissue of the septum). A torqueable, kink-resistant, shaped guiding catheter (not shown) can be loaded over theshaft1022 of thedelivery device1000 in order to provide additional means for steering thesensor1001 into position. The characteristics of this guiding catheter are that the outer diameter is small enough to fit within the introducer sheath, and the inner diameter is large enough to load over theshaft1022 of thedelivery device1000.
• Referring toFIG. 38, theshaft1022 of thedelivery device1000 is rotated in a clockwise direction to screw theanchor1004 of the sensor into thetissue1030 of the septum. When theanchor1004 has been fully inserted into thetissue1030, as shown inFIG. 39, thesensor1001 tightens against thewall1032 of the septum and creates a resistance. This resistance is sufficient to overcome the resistance between the reverse-threadedscrew1018 and the corresponding reverse-threadedbore1014 in thehousing1006 of theretention mechanism1005. Consequently, continued rotation of theshaft1022 of thedelivery device1000 in the clockwise direction will withdraw thescrew1018 from itsbore1014, as illustrated inFIG. 40. Once thescrew head1020 has cleared thesmooth counterbore1016 in the lower end of thehousing1006 of the retention mechanism, the lower ends of the twohousing halves1008,1010 return to their normal, closed configuration, thereby opening the upper ends of the two housing halves and releasing thesensor1001, as depicted inFIG. 41. Thedelivery device1000 is then withdrawn from the patient, leaving thesensor1001 anchored to thewall1032 of the septum with its pressure-sensing surface1003 facing outward.
• A feature of the disclosed embodiment is the use of a reverse-threadedscrew1018 andcorresponding bore1014 so that rotating theshaft1022 in a normal “tightening” direction will first screw the sensor into the wall of the septum and then open theretention mechanism1005 to release thesensor1001, all without having to reverse direction of rotation of the shaft. To permit this arrangement, it is necessary that thescrew1018 engage theretention mechanism1005 with enough mechanical force that the initial rotation of theshaft1022 will cause the sensor to screw into the wall of the septum, rather than withdraw thescrew1018 from theretention mechanism1005. In addition, it is also necessary that the screw be sufficiently loose with respect to the retention mechanism that once the sensor has completely screwed into the wall of the septum, the torque resistance will overcome the engagement between the screw and the retention mechanism rather than continue to rotate thesensor1001. This feature can be accomplished, for example, by controlling the tolerances between thescrew1018 and theretention mechanism1005, and by controlling the resilient force exerted by thehousing1006 against thehead1020 of the screw.
• FIGS. 42 and 43 illustrate an alternate embodiment of aretention mechanism1055. Theretention mechanism1055 is mounted to a flexible,torqueable shaft1022, just as in the previously disclosed embodiment. However, rather than theclamshell housing1006, theretention mechanism1055 comprises a plurality ofresilient wire fingers1056 extending upward from a base1058. Thefingers1056 of the disclosed embodiment are comprised of nitinol, though any suitable resilient biocompatible material can be used.Hooks1060 at the upper ends of thewire fingers1056 wrap around the upper edges of thebody1002 of thesensor1001. In the disclosed embodiment there are foursuch wire fingers1056 spaced 90° apart around the circumference of thecylindrical sensor body1002, although a greater or lesser number offingers1056 can be used. Only twofingers1056 are shown in the drawings for convenience of illustration.
• Aspreader1064 is disposed between thefingers1056. Thespreader1064 is attached to a pull-wire1066, which extends through the longitudinal opening of theshaft1022 and to a location outside of the patient. When the physician desires to release theretention mechanism1055 from thesensor1001, he simply exerts a tension on the pull-wire1066. In response, the spreader moves downward and biases thefingers1056 apart, releasing thesensor1001 from theretention mechanism1055. In the disclosed embodiment thespreader1064 is a circular disk or a frustocone, but it will be understood that any shape can be used which biases the fingers apart in response to tension applied to the pull-wire1066.
• By changing the anchoring means, the samebasic sensor1001 can be adapted for use within a lumen such as an artery or arteriole in the pulmonary artery vasculature.FIGS. 44-46 illustrate asensor1100 of the type described above. Thesensor1100 has awire loop1102 extending outward from thesensor body1104. As shown inFIG. 46, thewire loop1102 causes thesensor1100 to lodge within alumen1106, with the sensor located centrally within the lumen and allowing blood flow all around in the direction indicated by thearrow1108.
• A delivery apparatus1150 for securing, delivering and deploying animplant1100 having ananchoring mechanism1102 is shown inFIGS. 47-51. The various components of the delivery apparatus1150 are shown individually inFIGS. 47-50. As shown inFIG. 47, the delivery apparatus includes anelongated shaft1152 having proximal anddistal ends1153,1154 respectively. Theshaft1152 has amain lumen1155, which extends the length of the shaft. Aport1156 places themain lumen1155 in communication with the ambient at an intermediate location along theshaft1152. Asecondary lumen1157 includes aproximal portion1158 and a distal portion1159. Theproximal portion1158 extends along a partial length of theshaft1152 and terminates in aport1160 in the sidewall of the shaft. The distal portion1159 originates in a port1161 in the sidewall of the shaft and extends in a distal direction to anend1162.
• A tether wire,1163 shown inFIG. 48, is adapted to be slidably positioned within thesecondary lumen1157 of theshaft1152.
• Acore wire1164, shown inFIG. 49, is configured to be received within themain lumen1155 of theshaft1152 and provides stiffness to the delivery apparatus1150. Thecore wire1164 has a decreasing diameter toward its distal end1165, providing an increased flexibility in the distal end of the delivery apparatus1150. Thecore wire1164 is fixed in themain lumen1155 of theshaft1152 using adhesive, thermocompression, or any other suitable fixation means.
• Referring toFIG. 50, a conventional guide wire1166 is dimensioned to extend beyond thedistal end1154 of theshaft1152 and to be received within a distal portion of themain lumen1155 of the shaft.
• FIG. 51 shows the delivery apparatus1150 withsensor1100 mounted. Thecore wire1164 is disposed within themain lumen1155 of theshaft1152. The tether wire1163 extends through theproximal portion1158 of thesecondary lumen1157 of theshaft1152 and exits through theport1160 in the shaft sidewall. The tether wire1163 then is threaded through thebody1104 of thesensor1100 and passed into the port1161 and hence into the distal portion1159 of thesecondary lumen1157. The guidewire1166 extends alongside the proximal portion of theshaft1152 and enters themain lumen1155 of theshaft1152 at theport1156. The guidewire1166 then passes through the distal portion of themain lumen1155 and exits thedistal end1154 of theshaft1152.
• A vessel introducer is placed in an access site such as the right internal jugular vein, the subclavian artery, the right femoral vein, or any other suitable access site. Theguidewire1164 is inserted through the vessel introducer and guided to the target site using suitable medical imaging technology. The delivery apparatus1150 withsensor1100 mounted thereto is then threaded over the guidewire and inserted into the vessel introducer.
• After the delivery apparatus is in the vessel introducer, the apparatus is navigated over the guidewire to a deployment site in the pulmonary artery. Theimplant1100 is deployed by pulling thetether wire1160 proximally to disengage the implant from theshaft1152. The delivery apparatus and guidewire are then removed from the body.
• Theimplant1100 may then “float” through the narrowing pulmonary artery vasculature until it reaches a location at which the vessel is sufficiently narrow that the implant lodges within the vessel, as shown inFIG. 46. At that point the implant will be firmly anchored within the vasculature.
• In alternate embodiments (not shown), thesecondary lumen1157 of the introducer1150 can comprise a single, uninterrupted lumen having twoports1160,1161, rather than twoseparate lumen portions1158,1159. In addition, thesecondary lumen1157 can extend all the way through thedistal end1154 of theshaft1152, rather than terminating at anend1160 short of the distal end of the shaft.
• Finally, it will be understood that the preferred embodiment has been disclosed by way of example, and that other modifications may occur to those skilled in the art without departing from the scope and spirit of the appended claims.

Claims (33)

1. A method of manufacturing a sensor for in vivo applications, comprising the steps of:

providing first and second wafers of an electrically insulating material;

forming a recess in said first wafer;

forming a first capacitor plate in said recess of said first wafer;

forming a second capacitor plate in a corresponding region of said second wafer;

mutually imposing said first and second wafers such that said first and second capacitor plates are arranged in parallel, spaced-apart relation; and

affixing said first and second wafers to one another in said mutually imposed position.

2. The method ofclaim 1, comprising the further step of:

providing an inductor coil having first and second leads;

electrically coupling said first lead of said inductor coil to said first capacitor plate; and

electrically coupling said second lead of said inductor coil to said second capacitor plate.

3. The method ofclaim 2, wherein said inductor coil is immobilized with respect to said capacitor plates and changes in coil configuration.

4. The method ofclaim 3, where the method for coil immobilization comprises using wire of sufficient strength so the coil does not shift position relative to the capacitor plates.

5. The method ofclaim 3, where the method for coil immobilization comprises using a coil formed on a bobbin.

6. The method ofclaim 5, where the bobbin is comprised of a thermoplastic material and heated to encapsulate and/or adhere to the surface of the coil receiving trench.

7. The method ofclaim 5, where the bobbin is press fit to at least one surface of the coil receiving trench.

8. The method ofclaim 3, where the method for coil immobilization comprises use of a thermosetting or thermoplastic material applied to a pre-formed coil to impart additional stability to said coil.

9. The method ofclaim 8, where a thermosetting polymer is applied to at least one space between the coil and the coil receiving trench in liquid form and cured.

10. The method ofclaim 8, where at least one thermoplastic preform is inserted and heated to fill the gap between at least one space between the coil and the coil receiving trench.

11. The method ofclaim 1, further comprising the step of reducing the thickness of one of said wafers underlying at least a portion of a corresponding one of said capacitor plates, whereby said reduced thickness portion is more deflectable in response to changes in ambient pressure than the unreduced thickness of said one of said wafers.

12. The method ofclaim 1, comprising the further step of forming a recess in said corresponding region of said second wafer, and

wherein said step of forming a second capacitor plate in a corresponding region of said second wafer comprises the step of forming a second capacitor plate in said recess of said second wafer.

13. The method ofclaim 1, wherein said step of providing first and second wafers of an electrically insulating material comprises the step of providing first and second wafers of a material selected from the group consisting of fused silica, quartz, Pyrex, and sintered zirconia.

14. The method ofclaim 1, wherein said step of affixing said first and second wafers to one another in said mutually imposed position comprises the step of laser-cutting said mutually imposed wafers to reduce the sensor to its final size and to hermetically fuse the two wafers together.

15. The method ofclaim 14, wherein said step of laser-cutting said mutually imposed wafers comprises the step of controlling a laser to deliver a power sufficiently large to cut and fuse the wafers together, while at the same time being sufficiently small that the internal components of the sensor are not damaged by excessive heat.

16. The method ofclaim 15, wherein said step of controlling said laser to deliver a power sufficiently large to cut and fuse the wafers together, while at the same time being sufficiently small that the internal components of the sensor are not damaged by excessive heat, comprises the step of controlling said laser to have a peak wavelength of approximately 10 micrometers when the wafers are comprised of fused silica.

17. The method ofclaim 1, wherein said step of affixing said first and second wafers to one another comprises the step of bonding said first and second wafers together using glass frit.

18. The method ofclaim 1, wherein said step of affixing said first and second wafers to one another comprises the step of adhering said wafers to one another.

19. The method ofclaim 1, wherein said step of affixing said first and second wafers to one another comprises the step of bonding said wafers together using a process selected from the group consisting of gold compression bonding, laser bonding, and anodic bonding.

20. The method ofclaim 1, wherein said step of forming a first capacitor plate in said recess of said first wafer comprises the step of electroplating.

21. The method ofclaim 20, comprising the further step, subsequent to said step of electroplating, of polishing said plate using chemical/mechanical polishing to effect at least one of planarizing and reducing the height of said plate.

22. The method ofclaim 20, comprising the further step, subsequent to said step of electroplating, of chemically etching said plate by a selective etchant to reduce the height of said plate.

23. The method ofclaim 1, wherein said step of forming a first capacitor plate in said recess of said first wafer comprises the step of using physical vapor deposition to deposit a layer of metal.

24. The method ofclaim 23, comprising the further steps, subsequent to said step of using physical vapor deposition, of:

applying photoresist over at least a portion of said layer of metal;

using a mask to pattern said photoresist; and

selectively etching exposed portions of said photoresist to define a desired pattern.

25. The method ofclaim 1, wherein said capacitor plates are spaced apart by a distance of from 0.1 to 10 micrometers.

26. The method ofclaim 17, wherein said capacitor plates are spaced apart by a distance of from 0.1 to 2 micrometers.

27. A method of manufacturing a sensor for in vivo applications, comprising the steps of:

providing three wafers of an electrically non-conductive material;

forming first and second capacitor plates on an upper surface of a first of said three wafers;

forming a third capacitor plate on a lower surface of a second of said three wafers;

mutually imposing said first and second wafers such that said third capacitor plate is positioned in generally parallel, spaced-apart relation from said first and second capacitor plates;

positioning an inductor coil having first and second leads on top of an upper surface of said second wafer;

electrically connecting a first one of said inductor coil leads to said first capacitor plate;

electrically connecting a second one of said inductor coil leads to said second capacitor plate;

forming a cavity in a third of said three wafers sufficient to receive said inductor coil;

positioning said third wafer on top of said second wafer with said inductor coil being received within said cavity of said third wafer; and

bonding said second wafer to said first and third wafers.

28. The method ofclaim 27, wherein said step of forming a cavity in said third wafer comprises the step of forming a cavity which extends all the way through said third wafer, and wherein said method further comprises the step of:

providing a fourth wafer;

positioning said fourth wafer atop said third wafer so as to close off an upper end of said cavity; and

bonding said fourth wafer to said third wafer.

29. A method of manufacturing a sensor for in vivo applications, comprising the steps of:

forming a bottom plate on a wafer of electrically insulating material;

forming a sacrificial layer over said bottom plate;

forming a top plate on top of said sacrificial layer;

removing said sacrificial layer to leave said bottom and top plates in spaced-apart relation.

30. The method ofclaim 29, wherein said step of forming a top plate on top of said sacrificial layer comprises the steps of:

forming a seed layer on top of said sacrificial layer; and

depositing a metal on top of said seed layer to form said top plate.

31. A method of manufacturing a sensor for in vivo applications, comprising the steps of:

providing first and second wafers;

forming a recess in said first wafer;

forming a first plate in said recess of said first wafer;

forming a coil-receiving trench in an upper surface of said second wafer;

forming second and third plates on said upper surface of said second wafer within the perimeter of said coil-receiving trench;

providing an inductor coil having first and second leads;

positioning said inductor coil within said coil-receiving trench in said upper surface of said second wafer;

electrically connecting said first and second leads of said inductor coil to said second and third plates on said upper surface of said second wafer;

mutually imposing said first and second wafers such that said first plate in said recess of said first wafer is in parallel, spaced apart relation to said second and third plates on said upper surface of said second wafer; and

affixing said first and second wafers to one another in said mutually imposed position.

32. The method ofclaim 31, wherein said step of affixing said first and second wafers to one another in said mutually imposed position comprises the step of cutting said first and second wafers outside said coil-receiving trench such that said wafers are both cut and fused by the heat of said laser.

33. The method ofclaim 32, further comprising the steps of:

prior to said step of cutting said first and second wafers, forming a dicing trench in a lower surface of said second wafer outside said coil-receiving trench; and

wherein said step of cutting said first and second wafers outside said coil-receiving trench comprises the step of cutting said mutually imposed first and second wafers with a laser at a base of said dicing trench.

Images